Fix USB uframe rate on atsam3u
Fix USB uframe rate on atsam3u

When in high speed mode, the atsam3u hal drops start of frame SOF
interrupts. This causes a MICRO_SOF rate 1/8 slower than it should be
since SOF and MICRO_SOF never occur at the same time. This patch
fixes that problem by processing SOF interrupts in addition to
MICRO_SOF interrupts.

Note - When in USB test mode during the USB tests, the timing
occasionally caused the atsam3u to only receive SOF interrupts and no
MICRO_SOF interrupts for more than 10s at a time. When in this state
the CDC port would stop sending UART data to the host PC, since CDC IN
transfers are started on the start of frame handling which was only
triggered by a MICRO_SOF interrupt. This caused an intermittent serial
read timeout in the when running the all endpoint test. With the
addition of processing SOF interrupts, both types of frame interrupts
are handled, so frame handling can't be starved by too many of one
type.

sg-/DAPLink,sg-/DAPLink,google/DAPLink-port,google/DAPLink-port,google/DAPLink-port,google/DAPLink-port,sg-/DAPLink